The present invention relates to a dry, free flowing thermal insulation particularly suitable for installation in building sidewall cavities and attics. More specifically, the present invention relates to a thermal insulation including a major amount of granular thermal insulating material and a minor amount of fibrous thermal insulating material. This thermal insulation may conveniently be installed by auger feeding, blowing or pouring the thermal insulation into place.
Heretofore it was known to insulate building sidewall cavities and attics with many types of thermal insulating materials. Preformed insulation, e.g., fiber glass batts, is one conventional type of insulation used in such sidewall cavities and attics. The fiber glass batts are sized to fit between upright studs in a wall cavity or horizontal joists in an attic. While such fiber glass batts provide good insulation properties, e.g., an R value (in hr-ft.sup.2 -.degree.F/BTU) of about 11 or 12, installation of such fiber glass batts can be very difficult after construction of a building is completed, particularly for the sidewall cavities which are typically inaccessible after completion of the building. In older buildings it is increasingly desirable to augment the amount of thermal insulation in the sidewall cavities and the attic but it is very difficult to utilize fiber glass batts unless there is adequate access to these spaces.
For many years, one method of insulating buildings has been to blow or pour a fibrous insulating material into cavities, e.g., sidewall cavities and attics, of such buildings. One known type of insulation utilized for reinsulating sidewall cavities and attics comprises ground cellulose fiber, e.g., ground newsprint, which is combined or impregnated with fire resistant additives. The cellulose fiber insulation is blown or poured into place through small access holes into a sidewall cavity or ceiling area. However, although the cellulose fibers are typically treated with fire resistant resistant material, the cellulose fibers still tend to burn. This feature is especially hazardous since in building sidewall cavities, insulated electrical wires may in time become worn thereby exposing the inner metal wires to the surrounding thermal insulation. If the thermal insulation surrounding such wires, i.e., the ground cellulose material, promotes combustion serious fires may result.
U.S. Pat. No. 2,235,542 discloses the use of asbestos with such materials so as to provide fire resistance. This patent states that the insulating material is preferably a dry, flakey or fibrous material so as to form insulating air cells. The patent also states that a granular material can be included if it is of a size so that it does not prevent the formation of the insulating air cells. Another known method for minimizing the possiblity of fire uses a thermal insulating material which is fire resistant such as mineral wool or glass fibers. One difficulty with such fibrous materials is that fibrous clumps or fragments tend to "hang up" on conduits and wires when the insulation material is used in a sidewall cavity.
One conventional insulation utilized for reinsulating or retrofitting insulation in sidewall cavities and ceiling areas is a synthetic foam which is typically blown into place. One disadvantage of such foams is that they may melt or burn and under these conditions poisonous gases are often released. Furthermore, such foams are subject to shrinkage and/or expansion after installation. If the foam shrinks sufficiently, gaps and channels in the insulation may result thereby providing free passage of air through the cavity or space to be insulated and seriously diminishing the thermal insulation value of the foam. Excessive expansion of the foam may result in sufficient stress on the confining sidewalls so as to cause the sidewall material to buckle or warp.
U.S. Pat. No. 3,447,789 relates to using expanded perlite as an insulating material. The use of granular material alone as an insulating material has the disadvantage that if an access hole is formed in a sidewall cavity being insulated the granular insulation tends to flow freely through the hole until the cavity above the access hole is emptied.
It is an object of the present invention to overcome the disadvantages of the prior art insulation materials by providing a dry, free flowing thermal insulation which has excellent thermal insulating properties and which readily fills a cavity but has sufficient integrity so as to have very minimal flow after it has been installed.
Other objects and advantages of the present invention will be apparent from the following description, the accompanying drawings, and the appended claims.
Accordingly, the present invention provides a free flowing thermal insulation including a major portion of granular material having low thermal conductivity and a minor portion of a fibrous thermal insulating material.